The Delivery notes you add to an eBay order are now printed on the shipping label and commercial invoice for Orange Connex, SpeedPAK FedEx/DHL services. (For SpeedPAK DHL, it will be reflected only on the commercial invoice, not on the AWB)
Add it in the order page, under Delivery notes, before creating a shipping label.
For SpeedPAK FedEx/DHL, the Delivery note is limited to 100 characters maximum.
